Filter/separators have been used in the aviation fueling industry for decades. These devices generally contain filter cartridges which also act either as a coalescer or separator. The separators of the prior art typically comprise a fluoropolymer coated onto a metal screen which has been formed into a cylinder. The fluorocarbon coating imparts water repellency to the filter, thereby causing the water to separate from the filtered stream. However, the process for applying the coating, as well as the fluoropolymer coating itself, continue to be relatively expensive.
In an effort to improve separators, while at the same time making them more cost effective, other screen materials have been utilized in the recent prior art devices. Specifically, screens made from plastic materials have been favored. Plastic screens may be formed with more threads per square inch than metal screens, due to smaller filament diameters and more efficient manufacturing methods. Moreover, alternative hydrophobic coatings applied to plastic screens are generally silicone-based compounds which are less expensive than fluoropolymers.
Unfortunately, the plastic screens used in conventional separators suffer from an inherent characteristic which affects their utilization; i.e., a plastic screen is extremely flexible. It must be mechanically supported within the separator device in order to perform the functions of filtration and water separation without collapsing under the pressure created by the flow of fluid therethrough. The plastic screen must be held in a smooth, taunt, cylindrical configuration. This is typically accomplished by placing the cylindrical plastic screen over a perforated metal tube. Of course, the metal tube must contain sufficient perforations to allow a high flow rate of fluid therethrough, but not have an excessive number of perforations that would allow the metal tube and surrounding screen to collapse under the pressure caused by the flowing fluid. Conventional separators which utilize a plastic screen over a metal tube employ a sheet metal tube perforated so as to create approximately 55 to 60 percent open area. It is difficult to form a metal tube having a greater amount of perforated area, which also retains the rigidity required to support a surrounding plastic screen under operating conditions.
It would be desirable to prepare a separator cartridge made from plastic which has a high throughput, does not require a limiting internal metal support tube, and is easy to manufacture.